In a chemical industry, and in aluminum, gold and uranium ore processing plants compressed air operated mammoth-pipe (air-lift pump) fitted tanks with conical bottoms are used for the mixing and delivery of slurries. 300-1000 mm diameter mammoth pipes are arranged along the vertical axis of these tanks which frequently can have capacities of several thousand m.sup.3.
Compressed air of higher pressure than the static pressure (slurry head) existing at the inlet site is injected through an inlet head into the lower zone of the air lift pipe extending to the conical bottom of the tank.
The 5-7 bar compressed air in the form of dispersed bubbles enters the air-lift pipe through hydraulically dimensioned ports. The slurry-air mixture--, overcoming the various resistances, is carried upwardly by the effect of the difference of specific weights, then overflows on the upper flange of the mammoth pipe, and at least a certain part of it returns to the tank. Thus the slurry flows into the mammoth pipe at the bottom, while it flows out at the top; as a result the full volume of the slurry in the tank is mixed, preventing the solid phase from settling. In case of series connected slurry mixing tanks the slurry can be delivered in several known ways so that the unmixed slurry admitted continuously into the first tank of the line should leave the last tank in the state of mixed slurry.
The process described here has been generally used all over the world. The production of the 5-7 bar compressed air per 1000 m.sup.3 tank generally requires 20 kW electric power and very costly air compressors.
The size of the bubbles formed at the inlet head ranges 3-20 mm in an industrial scale unit. The bubbles of different sizes and shapes move with different ascendant velocities, large bubbles overtaking smaller ones, and the increased-volume bubbles incorporate along their paths the smaller ones by way of chain-reaction. When the speed of the large bubbles in the mammoth pipes is higher than that of the slurry resulting in greater slip, i.e. the mammoth pipe efficiency is reduced. The efficiency is likewise lowered by the fact that the bubbles rise along a spiral path causing undesirable eddy currents. Consequently in the long, 20-40 m high mammoth pipe used in the practice, the local efficiency diminishes upwards at a continuous rate, and on the outlet level it is not even 10%.